1. Field of the Invention
The invention concerns a plasma torch which projects into a vessel or container and is fastened at a supporting device and has a nozzle arranged at a burner lance, as well as a main electrode pipe with a main electrode arranged inside the burner lance, gaseous and liquid media as well as electric current being supplied to the main electrode via coaxially arranged pipes, wherein an annular insulating member is provided around the main electrode in the region of its foot end and encloses the electrode annularly, the outer wall or casing of the double-walled burner lance which is held by the supporting device being fastened at this insulating member, specifically for plasma torches with or without ignition lance.
2. Description of the Prior Art
Plasma torches are subjected to high thermal loading when used in containers. The main electrode is substantially acted upon thermally by electric current heat, while the casing of the burner lance is subjected to heat particularly from the melting bath, the furnace wall and the heat radiated from the arc. The resulting changes in temperature in the work materials cause considerable changes in length of the structural component parts.
A relative axial displacement of the main electrode and nozzle is caused particularly as a result of individual structural component parts of the plasma torch being acted upon thermally to varying degrees. These changes have a negative effect on the formation of the plasma arc. In plasma torches provided with ignition electrodes, comparable changes in length occur between the ignition electrode and the main electrode.
It is known from DE-OS 29 00 330 to cool the individual structural component parts of a plasma torch, namely the ignition electrode, the main electrode and the nozzle, independently of one another.
The plasma torch known from DE-OS 29 00 330 is not only expensive to produce, but also has hardly any influence on the set of problems relating to the relative displacement of the individual cooling structural component parts, since the lances are fixed in each instance at the portion of the burner remote of the melt. The individual lances can expand along their entire length with the result that the greatest axial displacements are to be found precisely in the critical region of the main electrode and nozzle.
A plasma torch is known from U.S. Pat. No. 3,463,957 in which the main nozzle and the main electrode are fixed in the region of the tip of the nozzle and are moreover connected to a common cooling water system.
The plasma torch known from this U.S. Patent is used for flame-cutting metal. Plasma torches of this type have no burner lances subjected to high heat radiation precisely when used in containers so as to result particularly in longitudinal expansion.
A plasma torch is known from DE 38 40 485 in which the ignition lance pipe is positioned within the main electrode pipe by centering sleeves. These centering sleeves serve for electric insulation and are therefore manufactured from plastic.
The plasma torch known from DE 38 40 485 forms a unit combining the ignition electrode and the ignition electrode pipe, which is not displaceable at the end remote of the ignition electrode.
It is the object of the present invention to provide a plasma torch which has a simple constructive design, operates in a reliable manner and with low maintenance when used at high temperatures and allows an adjustable, constant formation of the plasma arc.
This object is met by the invention in the characterizing part of claims I and 11.
Without recourse to a prototype, the present Inventor suggests a two-point bearing support of individual structural component parts of the plasma torch. In so doing, the structural component part which is thermally loaded to the highest degree, and accordingly also subject to the greatest changes in length of the structural component parts, acts as the supporting member. In the plasma torch according to the invention, this is the casing of the burner lance, whose foot end is held by the supporting device. The head end of the casing projecting into the furnace container forms the fixed point for the rest of the structural component parts.
one of these structural component parts is the main electrode pipe, the main electrode being fastened to its head end. The head end of the main electrode pipe is fixedly connected with the head end of the casing by means of an insulating member and forms the stationary bearing of the main lance. The foot end of the main lance is constructed as a movable bearing. As a result of this type of bearing support, the change in length of the structural component parts brought about by the thermal expansion can proceed without tension.
The sliding elements of the movable bearing of the main electrode pipe are constructed in such a way that a reliable transmission of the electric current is ensured. Contact springs which enclose the electrode pipe in the form of a bush are particularly suited to this purpose.
The water guidance arrangement of the plasma lance is constructed in such a way that fresh coolant is guided from the supporting device to the main electrode pipe and from there, in the interior of the pipe, to the main electrode. In the interior of the main electrode, the coolant is guided to the surfaces which are thermally loaded to the highest degree and after leaving the electrode is guided directly to the nozzle ring via overflows.
After suitable water guidance in the nozzle, the cooling water is guided back to the supporting device in the double-casing of the electrode lance.
Obviously, the necessary insulation is provided between the structural component parts of the burner. In the present invention, the insulation has been incorporated in the fixed point between the electrode and nozzle ring.
Plasma torches with ignition electrodes have their own bearing system with stationary and movable bearings for the ignition electrode. The fixed point is formed in the head region of the ignition electrode by an insulating bush.
Cooling water flows around the ignition electrode pipe over its entire length. During operation it is additionally cooled by gas flowing in the interior of the ignition lance. The change in length which occurs due to the current-generated heat in spite of the intensive cooling are absorbed by sliding elements arranged at the foot end of the ignition electrode pipe.
A quick-closing mechanism in which the media feed lines are arranged is arranged at the supporting arm for holding the plasma torch. The quick-closing mechanism is constructed so as to enable a simple and quick exchange of the plasma torch. The media feed lines from the supporting device and from the burner lance are adapted to one another and after closing the quick-closing mechanism ensure a reliable, trouble-free feed of gaseous and liquid media and electric current.